1. Field of the Invention
The present disclosure relates to a display device and a manufacturing method of a display device. More particularly, the present disclosure relates to a display device and a manufacturing method of a display device including an organic thin film transistor (O-TFT), where an organic semiconductor layer is provided.
2. Description of the Related Art
Thin film transistors (TFTs) are used as switch elements to control operation of display pixels, and as driver elements to drive the display pixels. TFTs are incorporated in a number of display types, such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, inorganic light emitting diode displays, flat panel displays, electro phoretic indication displays or the like. TFTs include a gate electrode, a gate insulating layer formed on the gate electrode, a semiconductor layer formed on the gate insulating layer, and a source electrode and a drain electrode which are separated from each other across the semiconductor layer to define a channel area.
Recently, as interest in flexible display devices has emerged, flat panel display designs using a plastic substrate have been studied. However, since flat panel displays using silicon as a semiconductor layer are manufactured at 300° C. or more, plastic substrates generally cannot be used. Therefore, an organic thin film transistor (O-TFT) using organic semiconductor material as the semiconductor layer instead of silicon is employed to manufacture flexible display devices.
Conventionally, the source electrode and the drain electrode are formed of metal such as gold (Au), palladium (Pd), platinum (Pt), or the like. These materials have a high work function, so that electric charges flow smoothly. However, source and drain structures using these metals are difficult to form by sputtering, and it is difficult to etch delicate patterns thereon. Thus, these materials are generally not compatible with the source electrode and drain electrode fabrication processes for O-TFTs.
On the other hand, conductive metal oxides, such as indium tin oxide (ITO) or indium zinc oxide (IZO), have the following advantages: their work function is high, ITO and IZO structures are easily formed using a sputtering method, and it is easy to form delicate patterns on ITO or IZO. Therefore, materials such as IZO and/or ITO are generally used for the source electrodes and the drain electrodes of O-TFTs instead of the aforementioned metal materials. However, ITO and IZO generate contact resistance at the contact interface with the organic semiconductor layer, thereby decreasing the drain current on-off ratio property of the TFT.